1. Field of the Invention
The present invention generally relates to field emitter arrays, and more particularly to a field emitter structure and fabrication process which provide venting of outgassed materials from the active electronic area of the structure.
2. Description of the Related Art
Field emitter arrays typically include a metal/insulator/metal film sandwich with a cellular array of holes through the upper metal and insulator layers, leaving the edges of the upper metal layer (which serves as an accelerator or gate electrode) effectively exposed to the upper surface of the lower metal layer (which serves as an emitter electrode). A plurality of conically-shaped electron emitter elements are mounted on the lower metal layer and extend upwardly therefrom such that their respective tips are located in respective holes in the upper metal layer. If appropriate voltages are applied between the emitter electrode, accelerator electrode, and an anode located above the accelerator electrode, electrons are caused to flow from the respective cone tips to the anode.
This structure is comparable to a triode vacuum tube, providing amplification of a signal applied to the accelerator or gate electrode, and operates best when the space in which the electrodes are mounted is evacuated. The three electrode configuration is known as a field emitting triode or "fetrode". However, numerous other applications for field emitter arrays have been proposed, including extremely high resolution flat panel television displays. A major advantage of the field emitter array concept is that the arrays can be formed by conventional photolithographic techniques used in the fabrication of integrated microelectronic circuits. This enables field emitter elements to be formed with submicron spacing, using process steps integrated with the formation of signal processing and other microelectronic circuitry on a single chip. A general presentation of field emitter arrays is found in an article entitled "The Comeback of the Vacuum Tube: Will Semiconductor Versions Supplement Transistors?", by Skidmore, Semiconductor International Industry News, pp. 15-18 (Aug. 1988).
A problem which has remained in conventional field emitter array structures involves the liberation of outgassed materials in the active electronic area of the device. During operation, electrons ejected from the field emitter tips strike the anode material, knocking off molecular particles of trapped gaseous and solid impurity materials. This outgassing effect creates a plasma or ionization in the spaces between the emitter tips and the anode, which seriously degrades the vacuum in the spaces and may cause arcing which can lead to destruction of the device.